Method of connecting together a plurality of transducer segments



July 8, 1969 c. MILLER 3,453,711

. METHOD OF CONNECTING TOGETHER A PLURALITY OF TRANSDUCER SEGMENTS FiledAug. 24, 1966 Sheet I of 2 0H Transducers IPolurizution L J J 1 i J 4654 58 42 50 92 82 e as 84 \V I I I r I 4 I I I I 70 I 5 &\\

76 Fig. 4 F /g. 5

INVENTOR.

' Irving 6. Miller 44%, i

July 8, 1969 c, WLLER 3,453,711

METHOD OF CONNECTING TOGETHER A PLURALITY OF TRANSDUCER SEGMENTS FiledAug. 24, 1966 Sheet ,8 of 2 PROVIDE SUBSTRATE, TRANSDUCERS, APERTUREDMASK AND LEAD WIRES APPLY A PLURALITY OF FIRST ELECTRODES TO SUBSTRATEBOND A TRANSDUCER TO EACH ELECTRODE APPLY A BACK ELECTRODE TO EACHTRANSDUCER PLACE APERTUFIED MASK OVER BACK ELECTRODES OF THE TRANSDUCERSDEPOSIT AN ELECTRICALLY CONDUCTIVE FILM THROUGH APERTURES ONTOELECTRODES REMOVE APERTURED MASK 1 ATTACH LEAD wIREs To INPUT AND OUTPUTELECTRODES F g. 6 INVENT OR.

Irving C. Miller BY f ga w fi A 7' TORNE Y United States Patent O METHODOF CONNECTING TOGETHER A PLURALITY OF TRANSDUCER SEGMENTS Irving C.Miller, Bradford, Pa., assignor to Corning Glass Works, Corning, N.Y., acorporation of New York Filed Aug. 24, 1966, Ser. No. 574,697 Int. Cl.B01j 17/00; H01l 1 5/ 02; H01c 7/08 U.S. Cl. 29--25.35 10 ClaimsABSTRACT OF THE DISCLOSURE A method for making improved connectionsbetween a plurality of adjacent, but separate, transducers or transducersegments. The transducers are bonded to a substrate by electrodes whichextend beyond the transducers so that terminals can be connected to theextended portions of the electrodes. Adjacent transducers areinterconnected by first applying a layer of insulating materialtherebetween and thereafter applying an electrically conductive materialover the insulating material so that it contacts electrodes on thesurface of the adjacent transducers.

The word transducer will hereinafter be used to designate a device madefrom a piezoelectric material; that is, a material which is capable oftransforming electrical energy into mechanical energy and which,conversely, is capable of transforming mechanical energy into electricalenergy. Transducers may be made from naturally occurring orartificial-1y produced crystalline materials. Titanates, zirconates,metaniobates and the like, in combination with various metal earthelements, are numbered among suitable artificial transducer materials.Broadly, such materials are known as ferroelectric ceramics. Crystals ofRochelle salts, quartz and the like are found to be suitable, naturallyoccurring, transducer materials. In recent art, artificially producedtransducer materials have assumed precedence over the naturalcrystalline materials, for reasons of improved efficiency, economy,reliability, and reproducibility.

A transducer must be electrically polarized before being placed inservice. Such polarization may be accomplished by several methods wellknown to one familiar with the art. One such method, for example, is toapply a direct current to a pair of electrodes deposited on oppositebroad faces of a slab of piezoelectric material, thereafter slices maybe removed from the slab and transducers fabricated therefrom.

In use, transducers must carry a pair of electrodes which serve aselectrical signal input or output means. Various methods of forming suchelectrodes are known, and, ordinarily, each electrode comprises one ormore thin, highly conductive, metallic films deposited on a substrate ofpiezoelectric material. One method of forming electrodes is taught inU.S. Patent No. 3,206,698 in the name of Richard E. Allen and George M.Deegan.

A transducer, with electrodes formed thereon, is usually bonded to abody of material through which it is desired to transmit, or from whichit is desired to receive, an acoustic energy wave. Such a body, forexample, may be a solid, plate type, acoustic delay line, with the transducer bonded to a facet there-of, but is not necessarily limitedthereto. Commonly, transducer electrodes play a part in the bondingprocess, which part is also described in the above-identified patent.Briefly, an electrode is used to for-m a portion of the mechanical bondbetween a transducer and a substrate. Electrical excitation of thetransducer is provided by attaching a polarized signal source, through apair of signal input terminals, to a corresponding pair of electrodes onthe transducer. In some instances, it is desirable to connect aplurality of transducers in electrical series with each other and withthe input signal source. For example, U.S. Patent 3,150,- 275, in thename of C. J. Lucy, teaches a sectional, series connected transducerwhich provides improved signal transfer capabilities, together withhigher eificieney, lower input terminal capacitance, and increasedradiation resistance.

In a power transducer, such as may be used on a photoelastic delay line,power and eificiency at the transducer are of prime importance. Sinceacoustic backings result in up to 50 percent power loss in the backingitself, which power loss is converted to heat that may deleteriouslyaffect the components, such power transducers are backed by employing athin metal film back electrode without any other backing materialthereby enabling virtually all of the energy being transmitted to belaunched into the delay line medium and be utilized. When a plurality ofsuch transducers have been employed it has been necessary tointerconnect them by soldering wires to the thin metal film electrodes.Such a solder forms spot acoustic backing thus resulting in lowertransducer efiiciency, heating and the like, in the area of the spot.When a plurality of connections have been made the effect is multiplied.Other transducers, however, have been intentionally backed when powertransmission is of secondary importance to performance parameters suchas band width, pulse characteristics and the like.

By acoustic loading of a transducer is meant the mechanical impedanceseen by either surface thereof. By acoustic backing is meant a materialapplied to a transducer, which material has the property of absorbingenergy.

In prior art transducer connection, the connecting wires provided weakmechanical connections and required careful handling. Furthermore, inpower transducers the solder would form spot backings that producedheating and resulted in transducer inefiiciency as heretofore described.In addition, with respect to some transducers, such connections would becostly, result in an unreliable product, and have an impractical inputimpedance.

It is therefore an object of the present invention to provide a methodwhereby the difficulties and problems hereinabove briefly described areovercome.

Another object of the present invention is to provide a means foreificiently interconnecting transducers, or segments thereof, to eachother and to a signal source.

Still another object of the present invention is to reduce spot loadingof transducers.

A further object of the present invention is to provide a means andmethod of coupling electrical energy to a transducer without causinglarge energy losses therein.

A still further object of the present invention is to provide a methodfor connecting together a plurality of transducer electrodes in apredetermined pattern,

These, together with other objects, features and advantages of thepresent invention will be more apparent from the following detaileddescription and drawing.

The present invention is a method of electrically connecting together ina predetermined manner a plurality of transducer electrodes comprisingthe following steps: providing a suitable substrate, and a plurality oftransducers; applying to said substrate a plurality of first electrodes,in adjacent spaced-apart relationship, said electrodes including asignal input electrode and a signal output electrode; bonding atransducer to each of said first electrodes and to said substrate;applying a back electrode to each of said transducers; depositing anelectrical insulating material between adjacent transducers toelectrically separate the electrodes of one transducer from theelectrodes of an adjacent transducer; selectively depositing anelectrically conductive material onto portions of the electrodes and theinsulating material thereby forming electrical connections between pairsof the electrodes in said predetermined manner; providing a pair of leadwires, and thereafter attaching one lead wire of said pair of lead wiresto said input electrode and the other lead Wire to said outputelectrode, thereby forming an array of electrically connectedtransducers.

FIGURE 1 is a fragmentary plan view of a pair of transducers bonded to asuitable substrate and electrically connected in series according to thepresent invention.

FIGURE 2 is a fragmentary, longitudinal cross section view of the delayline and transducers taken along line 2--2 of FIGURE 1.

FIGURE 3 is a plan view of a delay line facet showing a plurality oftransducers bonded thereto and electrically connected together in seriesin accordance with another embodiment of the present invention.

FIGURE 4 is a lateral cross section view of the delay line and atransducer taken along line 44 of FIG- URE 3.

FIGURE 5 is a fragmentary, cross-sectional view of a pair of transducersbonded to the facet of a delay line and electrically connected togetherin parallel in accordance with a further embodiment of the presentinvention.

FIGURE 6 is a flow diagram of the method of connecting together aplurality of transducers in accordance with the present invention.

In FIGURES 1 and 2 transducers 12 and 14 are bonded to a suitablesubstrate, such as facet 15 of delay line 16, by means of facetelectrodes 17 and 18. Back electrodes and 22, partially cut away inFIGURE 1 to reveal transducers 12 and 14 beneath, are electricallyconnected together by means of an electrically conducting film 24.Signal terminals 28 and 30 are attached to electrodes 17 and 18 by meansof lead wires 32 and 34 respectively. As may be seen in FIGURE 2,transducers 12 and 14 are separated by electrical insulating material 26which serves to electrically separate the transducers and also tosupport conducting film 24, which electrically connects the electrodestogether. Lead wires 32 and 34 are attached by any convenient means,such as soldering for example, to facet electrodes 17 and 18respectively.

The transducers may be made from suitable piezoelectric materials, suchfor example as one of the lead zirconate-titanate ceramics hereinbeforebriefly described. Delay line 16 may be a solid, plate type delay linemade from glass or fused silica, for example. Suitable transducer anddelay line materials may be readily selected by one familiar with theart. Facet 15 may be a signal input facet or a signal output facet ofthe delay line. Facet electrodes 17 and 18, and back electrodes 20 and22 are formed from one or more thin layers of metal film such as hasbeen described in the aforementioned Allen-Deegan patent. In addition,the back electrodes may have acoustic energy absorbing material bondedthereto for improved transducer response, as is well known to onefamiliar with the art.

Electrical insulation 26 is deposited on facet 15 of delay line 16,filling the gap between adjacent transducers 12 and 14. Electricalinsulation 26 is a material which adheres to the delay line and to thetransducers, is easily applied, and provides a solid mechanicalconnection between the transducers. Examples of suitable insulatingmaterials are organic coatings and lacquers, which may be applied byspraying, painting, flowing and similar methods, and which will dry inair at room temperature or upon baking at low temperature into tough,adhesive films. It has been found that a preferable material forelectrical insulation is an organic lacquer marketed by Bee ChemicalCompany, Lansing, 111., and known as Logo Clear ET 179 or M 5972. Thisparticular material is especially suitable for use with the process ofvacuum depositing metal films, since it does not outgas in vacuum andmetallic films readily adhere to it. It may be applied as a thin sprayedcoating, but is preferably applied by painting, to provide a relativelythick base for the vacuum evaporation of thin metallic films thereon.

Electrically conducting film 24 may be made from at least one layer ofhighly conductive material such as metal for example, but is preferablymade from a plurality of metallic layers vacuum evaporated on portionsof back electrodes 20 and 22, and on the surface of electricalinsulation 26, thereby electrically connecting electrode 20 to electrode22.

Examples of suitable metals for electrically conducting film 24 aregold, aluminum, combinations of nickel and chrome, and layeredcombinations thereof which provide high electrical conductivity andresistance to atmospheric oxidation. Signal input terminals 28 and 30are connected in series with transducers 12 and 14 by means of leadwires 32 and 34, facet electrodes 17 and 18, back electrodes 20 and 22,and electrically conducting film 24. Lead wires 32 and 34 may besoldered directly to their corresponding facet electrodes.

In FIGURE 3 a plurality of back electrodes including electrodes 40, 42,and 44 are series connected in a particular pattern on transducers whichare bonded to delay line 46 by means of conducting films 48, 50, and 52and facet electrodes 54, 56, and 58. Lead wires 60 and 62 are attachedto the input and output electrodes respectively. Dotted line 63illustrates the current flow path between input lead wire 60 and outputlead wire 62 through the various electrodes and transducers.

In FIGURE 4 back electrode 42 is bonded to transducer 43 which in turnis bonded to delay line 46 by means of facet electrode 54. Conductingfilm 50 is applied by vacuum evaporation, for example, to back electrode42, electrical insulation 64, and facet electrode 56, therebyelectrically connecting back electrode 42 of transducer 43 to facetelectrode 56 of an adjacent transducer. As will be immediately apparentby comparing the embodiment of FIGURE 4 with the embodiment shown inFIGURE 2, the electrical connection of FIGURE 4 provides another meansof series connecting transducer segments. Instead of electricalinsulation 64 filling a gap between transducers, it provides a slopingsurface, or ramp, to support an electrically conductive film such asfilm 50, for example, which joins the back electrode of one transducerto the facet electrode of an adjacent transducer.

FIGURE 5 illustrates a pair of transducers 70 and 72 electricallyconnected in parallel, and bonded to delay line 76. A common facetelectrode 74 is bonded to facet 75 of delay line 76. Signal input leadwire 78 is attached directly to facet electrode 74 at point 80. Backelectrodes 82 and 84 are bonded to transducers 70 and 72 respectively.Electrical insulation 86 mechanically joins, but electrically insulates,the transducers, providing a suitable base for application of electricalconducting film 88 which connects back electrode 82 to back electrode84. Output lead wire 90 is attached to back electrode 82 at point 92 byany convenient means such as soldering, for example. It should be notedthat when desired, electrodes 82 and 84 as well as film 88 could be ofintegral construction.

Series connection between transducers in the manner of the presentinvention has several major advantages which may be divided intomechanical advantages and electrical advantages. It will be seen inFIGURES 1, 2 and 3, for example, that the lead wires are attacheddirectly to the facet electrodes bonded to the delay line, rather thanto the back electrodes bonded to the more fragile transducers. Onedistinct mechanical advantage is that the lead wires are more solidlyattached, are only two in number, and at their points of attachment donot provide spot loading of the transducers. Heretofore, it has beennecessary to connect electrodes together by soldering connecting leadWires therebetween, thus creating the problem of spot loading at eachpoint of attachment to a back electrode. The reliability of electricaland mechanical connection between transducer electrodes is enhanced bythe present invention. A further mechanical advantage lies in the factthat a plurality of conducting films may be applied simnltaneouslybetween a plurality of electrodes, in a predetermined pattern, by vacuumevaporating a metallic film through, for example, a suitably aperturedmask whose apertures correspond to the desired location of theconducting films.

Electrically, a series connection between transducer electrodeseffectively lowers the terminal capacitance and effectively raises theterminal impedance of a delay line transducer as will hereinafter bedescribed in a typical example. It is not intended that the presentinvention be limited to series connections, however, since parallelcon-= nections may be desired for other purposes.

As shown in the flow diagram of FIGURE 6 which illustrates the steps ofthe method of the present invention, there is provided a delay linehaving a suitable facet to receive a plurality of transducers, and apair of lead wires. A plurality of electrically conducting facetelectrodes are deposited on the delay line facet in adjacentside-by-side relationship by a process of vacuum evaporation of one ormore metallic films. The transducers are bonded to the delay line facetsby means of the facet electrodes, each facet electrode having onetransducer bonded thereto. A back electrode is next applied to eachtransducer. =Electrical insulation is next deposited in the gap betweenadjacent transducers, or between a back electrode of one transducer anda facet electrode of adjacent transducer, whichever may be desired, ashas been heretofore described. A suitably apertured mask is next placedover the plurality of transducers in such a manner that the aperturesare disposed directly over the areas where the electrically conductingfilms are to be deposited. A plurality of electrically conducting filmsare simultaneously vacuum evaporated in the desired pattern through theapertures of the apertured mask, directly onto the surfaces of theelectrodes and the insulating material. Thereafter, a lead wire isattached to the signal input electrode and another lead wire is attachedto a signal output electrode, completing the connections.

In a typical example of the present invention, eighteen transducers,each about 0.1 inch wide, 0.6 inch long and 0.004 inch thick, arearranged in adjaent side-by-side relationship along the input facet of afused silica, plate type, ultrasonic delay line and are bonded theretoby corresponding facet electrodes formed of thin films of gold,chrome-nickel, nickel and indium. The transducers are made from aferroelectric ceramic material consisting essentially of about 45% PbTiOand 55% PbZrO by weight. The transducer electrodes are formed of thinfilms of nickel, chrome and gold to which the transducer back electrodematerial consisting essentially of 60% tin and 40% lead, is bonded tothe transducers by solder consisting essentially of 65% indium and 35%tin. Insulating material formed of the heretofore noted preferredorganic lacquer made by Bee Chemical Company is deposited between thetransducers by means of a small paint brush with a thin, pointed tip forpainting the material in place. A highly conductive nickel-chrome alloyfilm and a gold 6 film are successively vacuum evaporated onto the backelectrode through an apertured mask whose apertures are arranged in sucha manner as to provide a patterned deposit of conductive film on theelectrodes and on the surface of the insulating material, therebyconnecting the electrodes to each other and to the input terminals. Thepattern is similar to that shown in FIGURES 3 and 4 of the drawings. Asignal input lead wire is spot soldered to a first facet electrode atone end of the array of eighteen adjacently deposited electrodes, and anoutput lead wire is spot soldered to a last facet electrode at theopposite end of the array from the input electrode.

The terminal impedance of each transducer is about of an ohm, and theterminal capacitance of each electrode is about 166,000 picofarads.Connected in series as hereinabove described, the overall impedance ofthe array is about 12 ohms, while the terminal capacitance of the arrayis about 5 12picofarads.

Although the present invention has been described with respect tospecific details of certain embodiments thereof, it is not intended thatsuch details be limitations upon the scope of the invention exceptinsofar as set forth in the following claims.

What is claimed is: 1. A method of electrically connecting together, ina predetermined pattern, a plurality of transducer electrodes comprisingthe following steps:

providing a suitable substrate, a plurality of transducers, an aperturedmask whose apertures are disposed therein according to a predeterminedpattern,

applying to said substrate a plurality of first electrodes in adjacentspaced-apart relationship, said electrodes including a signal inputelectrode and a signal out: put electrode,

bonding a transducer to each of said first electrodes and to saidsubstrate,

applying a back electrode to each of said transducers,

depositing an electrical insulating material between adjacenttransducers to electrically separate the electrodes of one transducerfrom the electrodes of an adjacent transducer,

placing said apertured mask over said transducers and the respectiveback electrode thereof so that said predetermined pattern of aperturescorresponds to a desired location on said back electrodes and said firstelectrodes,

depositing an electrically conductive material through said aperturesonto said electrodes, thereby forming electrical connections betweensaid electrodes in ac=- cordance with said predetermined pattern,

removing said apertured mask,

providing a pair of lead wires, and

attaching one lead wire to said pair to said input electrode and theother lead wire to said output electrode, thereby forming an array ofelectrically connected transducers.

2. The method of claim 1 wherein said substrate is a signal input facetof an acoustic delay line.

3. The method of claim 2 wherein said first electrodes are metallicfilms deposited on said signal input facet.

4. The method of claim 3 wherein said back electrodes include acousticabsorbing material.

5. The method of claim 4 wherein said electrically insulating materialis deposited by painting.

6. The method of claim 4 wherein said electrically insulating materialis deposited by spraying.

7. The method of claim 5 wherein said electrically conductive materialis deposited through said apertures by vacuum evaporation.

8. A method of electrically connecting a plurality of transducerscomprising the steps of:

providing a substrate and a plurality of transducers,

applying to said substrate a plurality of first electrodes in adjacentspaced relationship,

bonding one of said transducers to each of said electrodes respectively,

disposing electrical insulating material between adjacent transducers,

applying a back electrode to each of said transducers,

and

applying an electrically conductive material over a predeterminedportion of said electrically insulating material in electrical contactwith the back electrodes of adjacent transducers.

9. The method of claim 8 wherein said back electrodes and saidelectrically conductive material are integral.

10. The method of claim 8 wherein said electrically insulating materialis disposed between adjacent transducers by filling the gap betweenadjacent transducers with a liquid insulating material and drying saidinsulating material to form a tough, adhesive film, and wherein saidelectrically conductive material is applied by placing an apertured maskover said transducers and electrodes and thereafter depositing saidelectrically conductive material through the apertures in said mask toform electrical connections between the electrodes in accordance with apredetermined pattern.

References Cited UNITED STATES PATENTS CHARLIE T. MOON, PrimaryExaminer.

D. C. REILEY, Assistant Examiner.

US. Cl. X.R. 29572, 578; 3108

